Infertility is a common heath problem that affects 10-15% of reproductive-age couples. A major cause of infertility is the production of few or no germ cells. However, today's treatments for infertility are largely ineffective in cases in which infertility is due to few or no germ cells. Little is known about the genes that regulate the production of germ cells or the factors that contribute to the block in differentiation of germ cells in infertile individuals. The elucidation of pathways and factors involved in germ cell differentiation, and the identification of agents that promote germ cell development and differentiation, is therefore of clinical and research interest. The present invention addresses these issues.